The present invention relates to a seal system for a transmission, and more particularly, the invention relates to a seal system for a shift shaft of an auxiliary box.
Transmissions for commercial vehicles have a large number of gears through which the vehicle operator shifts as the vehicle travels under various load and grade conditions. The transmission may be manual or automated manual. A typical commercial vehicle transmission includes a main gear box through which the operator shifts using a transmission shift lever. An auxiliary gear box is attached to the main gear box to provide gear ratios in addition to those provided by the main gear box. The gears of the auxiliary gear box may be shifted with hydraulic or pneumatic actuators in response to the vehicle operator manipulating electronic buttons or switches in the vehicle cab.
For auxiliary gear boxes utilizing pneumatic actuators, a piston housing is secured to the auxiliary gear box. Solenoids are connected to the piston housing and control the flow of air into the piston housing to drive a piston. The actuator includes a shift shaft with the piston secured thereto. The piston disposed within an air chamber. The shift shaft is supported by the auxiliary gear box, and the piston may be arranged in either the auxiliary gear box or piston housing. The solenoids control the flow of air to either side of the piston to move the shift shaft axially. The shift shaft includes a shift fork supported thereon which engages a clutch collar in the auxiliary gear box that selectively engages the auxiliary gears in response to axial movement of the piston.
A seal is used between the shift shaft and auxiliary box housing to separate the pressurized air within the air chamber and the transmission oil within the auxiliary gear box. An annular groove is machined into the bore of the auxiliary box housing supporting the shift shaft. Typically, an O-ring is arranged within the annular groove. Because the annular groove is located within the bore, it is difficult to machine. Moreover, the O-ring may not provide an acceptable seal. Therefore, what is needed is an improved seal system for an auxiliary gear box housing that is easier to machine and provides a more effective seal.